Implantable medical devices (IMDs) are devices designed to be implanted into a patient. Some examples of these devices include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), cardiac resynchronization devices, and devices that include a combination of such capabilities. The devices are typically used to treat patients using electrical or other therapy and to aid a physician or caregiver in patient diagnosis through internal monitoring of a patient's condition. The devices may include one or more electrodes in communication with sense amplifiers to monitor electrical heart activity within a patient, and often include one or more sensors to monitor one or more other internal patient parameters. In general, the sensors convert sensed internal parameters into electrical signals. The electrical signals monitored within the patient and the electrical signals from the sensors can be quantized by analog-to-digital converters and stored in the IMD as data. Other examples of implantable medical devices include implantable diagnostic devices, implantable insulin pumps, devices implanted to administer drugs to a patient, or implantable devices with neural stimulation capability.
IMDs are able to communicate with external devices using wireless communication methods. The external devices are often external programmers that use wireless communication links to change performance parameters in the implantable device. The IMD also wirelessly transmits stored data obtained from sensors to an external device. The external device may then display the collected data on a computer screen display or a strip chart recorder.
As technology used in IMDs advances, the devices are able to collect data from multiple sensors at multiple locations. They also detect events occurring from such multiple sources. Because the data may be collected from different types of sensors, the data may be dissimilar from one sensor to the next. Also, the data may be collected at different times and/or sampling rates. The large amount of data coming from various sources complicates the task of reconstructing the information for a display while preserving the correct relationships among the data.